Neurochemical and electrophysiological deficits in the ventral hippocampus and selective behavioral alterations caused by high-fat diet in female C57BL/6 mice

The metabolic and neuroinflammatory changes induced by consuming a cafeteria diet are age-dependent

OBJECTIVES

To compare the effects of a palatable cafeteria diet on serum parameters and neuroinflammatory markers of young and aged female Wistar rats.

METHODS

Three-month-old (young) and 18-month-old (aged) female Wistar rats had access to a cafeteria diet (Caf-Young, Caf-Aged) or a standard chow diet (Std-Young, Std-Aged).

RESULTS

The Caf-Young group showed a higher food consumption, weight gain, visceral fat depot, serum insulin and leptin levels, and the insulin resistance index (HOMA-IR) than the Std-Young group. The Caf-Aged group exhibited an increase in interleukin-1 levels in the cerebral cortex and hippocampus. The number of GFAP-positive cells did not differ between the groups, but there was a diet effect in the cerebral cortex and an age effect in the hippocampus. Phospho-tau expression did not differ between the groups.

DISCUSSION

The 3- and 18-month-old rats responded differently to a cafeteria diet. Insulin and leptin levels are elevated in young animals fed a cafeteria diet, whereas aged animals are prone to neuroinflammation (indicated by an increase in interleukin-1β levels). A combination of hypercaloric diet and senescence have detrimental effects on the inflammatory response in the brain, which may predispose to neurological diseases.

Age-Dependent Responses of Brain Myelin Integrity and Behavioral Performance to Radiation in Mice

Radiation therapy is widely used to treat primary and metastatic brain tumors, but it may also lead to delayed neurological complications. Oligodendrocytes in the central nervous system produce myelin, and myelin integrity becomes highly vulnerable after brain irradiation. In this study, mice at different developmental stages were used to test the age-dependent sensitivity of myelin formation and maintenance, as well as behavioral performance after whole-brain irradiation (WBI). Mice at postnatal days 21 and 28 and at 2 months received a single dose of 25 Gy WBI. Behavioral tests for general locomotor activity and motor coordination revealed an age-dependent response after WBI. Quantitative observation revealed a sharp decrease in the number of oligodendrocytes beginning at day 1 after WBI, which recovered during different observation intervals in white matter and gray matter in mice of different ages. Myelin basic protein (MBP) staining revealed disparate quantities in an age- and brain-region-dependent pattern between groups after WBI, which was confirmed using Black-Gold staining. In summary, the response to radiation in mice of different ages provided insight into the potential of oligogenesis in microenvironments at respective stages of myelin regeneration, which may reduce central nervous system impairment and optimize the prognosis after radiation treatment.

Autism-Like Behaviours and Memory Deficits Result from a Western Diet in Mice

Nonalcoholic fatty liver disease, induced by a Western diet (WD), evokes central and peripheral inflammation that is accompanied by altered emotionality. These changes can be associated with abnormalities in social behaviour, hippocampus-dependent cognitive functions, and metabolism. Female C57BL/6J mice were fed with a regular chow or with a WD containing 0.2% of cholesterol and 21% of saturated fat for three weeks. WD-treated mice exhibited increased social avoidance, crawl-over and digging behaviours, decreased body-body contacts, and hyperlocomotion. The WD-fed group also displayed deficits in hippocampal-dependent performance such as contextual memory in a fear conditioning and pellet displacement paradigms. A reduction in glucose tolerance and elevated levels of serum cholesterol and leptin were also associated with the WD. The peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1a) mRNA, a marker of mitochondrial activity, was decreased in the prefrontal cortex, hippocampus, hypothalamus, and dorsal raphe, suggesting suppressed brain mitochondrial functions, but not in the liver. This is the first report to show that a WD can profoundly suppress social interactions and induce dominant-like behaviours in naïve adult mice. The spectrum of behaviours that were found to be induced are reminiscent of symptoms associated with autism, and, if paralleled in humans, suggest that a WD might exacerbate autism spectrum disorder.

The behavioral and physiological effects of high-fat diet and alcohol consumption: Sex differences in C57BL6/J mice

BACKGROUND AND OBJECTIVE

Animal studies can be a great tool to investigate sex differences in a variety of different ways, including behavioral and physiological responses to drug treatments and different "lifestyle variables" such as diets. Consumption of both high-fat diets and alcohol is known to affect anxiety behaviors and overall health. This project investigated how high-fat diet and alcohol access and its combination affected the behavior and physiology of male and female C57BL/6J mice.

METHOD

Mice were separated into three food groups: high-fat diet, 10% fat diet, and regular chow, and each group was paired with either water or 10% alcohol. Behavioral assays included diet and alcohol preference, light-dark box, open field, and feeding and drinking measurements. Physiological measures included glucose tolerance tests and measurement of brain-derived neurotrophic factor, insulin, and leptin levels.

RESULTS

Females and males differed in the open field, as male mice decreased activity, while females increased activity when consuming high-fat diet. While females consumed more ethanol than males, alcohol consumption was able to improve glucose tolerance and increase anxiety in both sexes. Lastly, females were more resistant to the physiological changes caused by high-fat diet than males, as females consuming high-fat diet exhibited decreased insulin secretion, less change to brain-derived neurotrophic factor levels, and better glucose tolerance than males consuming high-fat diet.

CONCLUSION

These results suggest that the response to high-fat diet and alcohol consumption is sex dependent and that males are more affected both behaviorally and physiologically by high-fat diet compared to females.

Utility and reliability of non-invasive muscle function tests in high-fat-fed mice

NEW FINDINGS

What is the central question of this study? Non-invasive muscle function tests have not been validated for use in the study of muscle performance in high-fat-fed mice. What is the main finding and its importance? This study shows that grip strength, hang wire and four-limb hanging tests are able to discriminate the muscle performance between chow-fed and high-fat-fed mice at different time points, with grip strength being reliable after 5, 10 and 20 weeks of dietary intervention. Non-invasive tests are commonly used for assessing muscle function in animal models. The value of these tests in obesity, a condition where muscle strength is reduced, is unclear. We investigated the utility of three non-invasive muscle function tests, namely grip strength (GS), hang wire (HW) and four-limb hanging (FLH), in C57BL/6 mice fed chow (chow group, n = 48) or a high-fat diet (HFD group, n = 48) for 20 weeks. Muscle function tests were performed at 5, 10 and 20 weeks. After 10 and 20 weeks, HFD mice had significantly reduced GS (in newtons; mean ± SD: 10 weeks chow, 1.89 ± 0.1 and HFD, 1.79 ± 0.1; 20 weeks chow, 1.99 ± 0.1 and HFD, 1.75 ± 0.1), FLH [in seconds per gram body weight; median (interquartile range): 10 weeks chow, 2552 (1337-4964) and HFD, 1230 (749-1994); 20 weeks chow, 2048 (765-3864) and HFD, 1036 (717-1855)] and HW reaches [n; median (interquartile range): 10 weeks chow, 4 (2-5) and HFD, 2 (1-3); 20 weeks chow, 3 (1-5) and HFD, 1 (0-2)] and higher falls [n; median (interquartile range): 10 weeks chow, 0 (0-2) and HFD, 3 (1-7); 20 weeks chow, 1 (0-4) and HFD, 8 (5-10)]. Grip strength was reliable in both dietary groups [intraclass correlation coefficient (ICC) = 0.5-0.8; P < 0.05], whereas FLH showed good reliability in chow (ICC = 0.7; P < 0.05) but not in HFD mice after 10 weeks (ICC < 0.5). Our data demonstrate that non-invasive muscle function tests are valuable and reliable tools for assessment of muscle strength and function in high-fat-fed mice.

A maternal diet high in saturated fat impairs offspring hippocampal function in a sex-specific manner

While a maternal diet high in saturated fat is likely to affect foetal brain development, whether the effects are the same for male and female offspring is unclear. As a result, we randomly assigned female, Sprague-Dawley rats to either a control, or high-fat diet (HFD; 45% of calories from saturated fat) for 10 weeks. A range of biometrics were collected, and hippocampal function was assessed at both the tissue level (by measuring synaptic plasticity) and at the behavioural level (using the Morris water maze; MWM). Subsequently, a subset of animals was bred and remained on their respective diets throughout gestation and lactation. On post-natal day 21, offspring were weaned and placed onto the control diet; biometrics and spatial learning and memory were then assessed at both adolescence and young adulthood. Although the HFD led to changes in the maternal generation consistent with an obese phenotype, no impairments were noted at the level of hippocampal synaptic plasticity, or MWM performance. Unexpectedly, among the offspring, a sexually dimorphic effect upon MWM performance became apparent. In particular, adolescent male offspring displayed a greater latency to reach the platform during training trials and spent less time in the target quadrant during the probe test; notably, when re-examined during young adulthood, the performance deficit was no longer present. Overall, our work suggests the existence of sexual dimorphism with regard to how a maternal HFD affects hippocampal-dependent function in the offspring brain.

Western High-Fat Diet Consumption during Adolescence Increases Susceptibility to Traumatic Stress while Selectively Disrupting Hippocampal and Ventricular Volumes

Psychological trauma and obesity co-occur frequently and have been identified as major risk factors for psychiatric disorders. Surprisingly, preclinical studies examining how obesity disrupts the ability of the brain to cope with psychological trauma are lacking. The objective of this study was to determine whether an obesogenic Western-like high-fat diet (WD) predisposes rats to post-traumatic stress responsivity. Adolescent Lewis rats (postnatal day 28) were fed ad libitum for 8 weeks with either the experimental WD diet (41.4% kcal from fat) or the control diet (16.5% kcal from fat). We modeled psychological trauma by exposing young adult rats to a cat odor threat. The elevated plus maze and the open field test revealed increased psychological trauma-induced anxiety-like behaviors in the rats that consumed the WD when compared with control animals 1 week after undergoing traumatic stress (p < 0.05). Magnetic resonance imaging showed significant hippocampal atrophy (20% reduction) and lateral ventricular enlargement (50% increase) in the animals fed the WD when compared with controls. These volumetric abnormalities were associated with behavioral indices of anxiety, increased leptin and FK506-binding protein 51 (FKBP51) levels, and reduced hippocampal blood vessel density. We found asymmetric structural vulnerabilities to the WD, particularly the ventral and left hippocampus and lateral ventricle. This study highlights how WD consumption during adolescence impacts key substrates implicated in post-traumatic stress disorder. Understanding how consumption of a WD affects the developmental trajectories of the stress neurocircuitry is critical, as stress susceptibility imposes a marked vulnerability to neuropsychiatric disorders.

Adolescent Maturational Transitions in the Prefrontal Cortex and Dopamine Signaling as a Risk Factor for the Development of Obesity and High Fat/High Sugar Diet Induced Cognitive Deficits

Adolescence poses as both a transitional period in neurodevelopment and lifestyle practices. In particular, the developmental trajectory of the prefrontal cortex (PFC), a critical region for behavioral control and self-regulation, is enduring, not reaching functional maturity until the early 20 s in humans. Furthermore, the neurotransmitter dopamine is particularly abundant during adolescence, tuning the brain to rapidly learn about rewards and regulating aspects of neuroplasticity. Thus, adolescence is proposed to represent a period of vulnerability towards reward-driven behaviors such as the consumption of palatable high fat and high sugar diets. This is reflected in the increasing prevalence of obesity in children and adolescents as they are the greatest consumers of “junk foods”. Excessive consumption of diets laden in saturated fat and refined sugars not only leads to weight gain and the development of obesity, but experimental studies with rodents indicate they evoke cognitive deficits in learning and memory process by disrupting neuroplasticity and altering reward processing neurocircuitry. Consumption of these high fat and high sugar diets have been reported to have a particularly pronounced impact on cognition when consumed during adolescence, demonstrating a susceptibility of the adolescent brain to enduring cognitive deficits. The adolescent brain, with heightened reward sensitivity and diminished behavioral control compared to the mature adult brain, appears to be a risk for aberrant eating behaviors that may underpin the development of obesity. This review explores the neurodevelopmental changes in the PFC and mesocortical dopamine signaling that occur during adolescence, and how these potentially underpin the overconsumption of palatable food and development of obesogenic diet-induced cognitive deficits.

Diet-induced obesity prolongs neuroinflammation and recruits CCR2(+) monocytes to the brain following herpes simplex virus (HSV)-1 latency in mice

Herpes simplex virus (HSV)-1 is a ubiquitous human infection, with increased prevalence in obese populations. Obesity has been linked to increased inflammation, susceptibility to infection, and higher rates of anxiety disorder and cognitive impairment. To determine how obesity alters neuroinflammation and behavior following infection, we infected weanling C57BL/6 or CCR2(RFP/+)/CX3CR1(GFP/+) mice with a very low dose of HSV-1. Following viral latency (14days post infection (d p.i.)), mice were randomly assigned to remain on the low fat (LF) diet or switched to a 45% high fat (HF) diet. Eight weeks post diet shift, latently infected mice on the HF diet (HSV-HF) had greater microglial activation and infiltration of inflammatory CCR2(+) monocytes in the hypothalamus and dentate gyrus, in comparison to both HSV-LF mice and uninfected mice on LF and HF diets. VCAM staining was present in hypothalamus and hippocampus of the HSV-HF mice in the areas of monocyte infiltration. Infiltrating monocytes also produced proinflammatory cytokines demonstrating that, along with activated microglia, monocytes contribute to sustained neuroinflammation in latently infected obese mice. Utilizing a light-dark preference test, we found that HSV-HF mice had increased anxiety-like behavior. In the marble-burying test, HF diet and HSV infection resulted in increased numbers of buried marbles. Together, these mice provide a useful, testable model to study the biobehavioral effects of obesity and latent HSV-1 infection in regards to anxiety and may provide a tool for studying diet intervention programs in the future.

The Outward Spiral: A vicious cycle model of obesity and cognitive dysfunction

Chronic failure to suppress intake during states of positive energy balance leads to weight gain and obesity. The ability to use context - including interoceptive satiety states - to inhibit responding to previously rewarded cues appears to depend on the functional integrity of the hippocampus. Recent evidence implicates energy dense Western diets in several types of hippocampal dysfunction, including reduced expression of neurotrophins and nutrient transporters, increased inflammation, microglial activation, and blood brain barrier permeability. The functional consequences of such insults include impairments in an animal's ability to modulate responding to a previously reinforced cues. We propose that such deficits promote overeating, which can further exacerbate hippocampal dysfunction and thus initiate a vicious cycle of both obesity and progressive cognitive decline.

A diet high in fat and sugar reverses anxiety-like behaviour induced by limited nesting in male rats: Impacts on hippocampal markers

Stress exposure during early development is known to produce long-term mental health deficits. Stress promotes poor lifestyle choices such as poor diet. Early life adversity and diets high in fat and sugar (HFHS) are known to affect anxiety and memory. However additive effects of HFHS and stress during early development are less explored. Here, we examined whether early life stress (ELS) simulated by limited nesting (LN) induces anxiety-like behaviour and cognitive deficits that are modulated by HFHS diet. We examined key hippocampal markers involved in anxiety and cognition, testing the hypothesis that post-weaning HFHS following ELS would ameliorate anxiety-like behaviour but worsen memory and associated hippocampal changes. Sprague-Dawley rats were exposed to LN, postnatal days 2-9, and at weaning, male siblings were given unlimited access to chow or HFHS resulting in (Con-Chow, Con-HFHS, LN-Chow, LN-HFHS, n=11-15/group). Anxiety-like behaviour was assessed by Elevated Plus Maze (EPM) at 10 weeks and spatial and object recognition tested at 11 weeks of age. Rats were culled at 13 weeks. Hippocampal mRNA expression was measured using TaqMan(®) Array Micro Fluidic cards (Life Technologies). As expected HFHS diet increased body weight; LN and control rats had similar weights at 13 weeks, energy intake was also similar across groups. LN-Chow rats showed increased anxiety-like behaviour relative to control rats, but this was reversed by HFHS diet. Spatial and object recognition memory were unaltered by LN exposure or consumption of HFHS diet. Hippocampal glucocorticoid receptor (GR) protein was not affected by LN exposure in chow rats, but was increased by 45% in HFHS rats relative to controls. Hippocampal genes involved in plasticity and mood regulation, GSKα and GSKβ were affected, with reductions in GSKβ under both diet conditions, and reduced GSKα only in LN-HFHS versus Con-HFHS. Interestingly, HFHS diet and LN exposure independently reduced expression of Akt3 mRNA, a key gene involved post-natal brain development. In summary, while an energy rich diet ameliorated anxiety-like behaviour induced by LN exposure, it significantly altered key genes that are essential for hippocampal development.

Voluntary wheel-running attenuates insulin and weight gain and affects anxiety-like behaviors in C57BL6/J mice exposed to a high-fat diet

It is widely accepted that lifestyle plays a crucial role on the quality of life in individuals, particularly in western societies where poor diet is correlated to alterations in behavior and the increased possibility of developing type-2 diabetes. While exercising is known to produce improvements to overall health, there is conflicting evidence on how much of an effect exercise has staving off the development of type-2 diabetes or counteracting the effects of diet on anxiety. Thus, this study investigated the effects of voluntary wheel-running access on the progression of diabetes-like symptoms and open field and light-dark box behaviors in C57BL/6J mice fed a high-fat diet. C57BL/6J mice were placed into either running-wheel cages or cages without a running-wheel, given either regular chow or a high-fat diet, and their body mass, food consumption, glucose tolerance, insulin and c-peptide levels were measured. Mice were also exposed to the open field and light-dark box tests for anxiety-like behaviors. Access to a running-wheel partially attenuated the obesity and hyperinsulinemia associated with high-fat diet consumption in these mice, but did not affect glucose tolerance or c-peptide levels. Wheel-running strongly increased anxiety-like and decreased explorative-like behaviors in the open field and light-dark box, while high-fat diet consumption produced smaller increases in anxiety. These results suggest that voluntary wheel-running can assuage some, but not all, of the physiological problems associated with high-fat diet consumption, and can modify anxiety-like behaviors regardless of diet consumed.

High-fat diet feeding alters olfactory-, social-, and reward-related behaviors of mice independent of obesity

OBJECTIVE

High-fat diet (HFD) consumption causes obesity, which is associated with well-known increased health risks. Moreover, obesity has been associated with altered sensorimotor and emotional behaviors of humans and mice. This study attempted to dissociate the influence of HFD-induced obesity on behaviors from the influence of HFD consumption itself.

METHODS

C57BL male mice were randomly allocated to a low-fat diet (LFD) group, an HFD-induced obesity (DIO) group, or a pair-fed HFD-feeding nonobese (HFD) group. A comprehensive behavioral test battery was performed on all three groups to assess sensorimotor functions, anxiety- and depression-like behaviors, reward-related behaviors, social behaviors, and learning/memory functions.

RESULTS

Both the DIO and HFD groups exhibited disturbed olfaction, blunted ethanol preference, and enhanced social interactions. The DIO group exhibited blunted sucrose preference, shorter latency before falling off during the rotarod test, and a lower response to mechanical stimuli.

CONCLUSIONS

The HFD-fed nonobese mice showed altered behaviors related to olfaction, social interactions, and rewards that were similar to those of the DIO mice. This finding suggests that HFD consumption alters a variety of behaviors independent of obesity.

Nutrition and Bipolar Depression

As with physical conditions, bipolar disorder is likely to be impacted by diet and nutrition. Patients with bipolar disorder have been noted to have relatively unhealthy diets, which may in part be the reason they also have an elevated risk of metabolic syndrome and obesity. An improvement in the quality of the diet should improve a bipolar patient's overall health risk profile, but it may also improve their psychiatric outcomes. New insights into biological dysfunctions that may be present in bipolar disorder have presented new theoretic frameworks for understanding the relationship between diet and bipolar disorder.

Time-dependent behavioral, neurochemical, and metabolic dysregulation in female C57BL/6 mice caused by chronic high-fat diet intake

High-fat diet (HFD) induced obesity is associated not only with metabolic dysregulation, e.g., impaired glucose homeostasis and insulin sensitivity, but also with neurological dysfunction manifested with aberrant behavior and/or neurotransmitter imbalance. Most studies have examined HFD's effects predominantly in male subjects, either in the periphery or on the brain, in isolation and after a finite feeding period. In this study, we evaluated the time-course of selected metabolic, behavioral, and neurochemical effects of HFD intake in parallel and at multiple time points in female (C57BL/6) mice. Peripheral effects were evaluated at three feeding intervals (short: 5-6 weeks, long: 20-22 weeks, and prolonged: 33-36 weeks). Central effects were evaluated only after long and prolonged feeding durations; we have previously reported those effects after the short (5-6 weeks) feeding duration. Ongoing HFD feeding resulted in an obese phenotype characterized by increased visceral adiposity and, after prolonged HFD intake, an increase in liver and kidney weights. Peripherally, 5 weeks of HFD intake was sufficient to impair glucose tolerance significantly, with the deleterious effects of HFD being greater with prolonged intake. Similarly, 5 weeks of HFD consumption was sufficient to impair insulin sensitivity. However, sensitivity to insulin after prolonged HFD intake was not different between control, low-fat diet (LFD) and HFD-fed mice, most likely due to age-dependent decrease in insulin sensitivity in the LFD-fed mice. HFD intake also induced bi-phasic hepatic inflammation and it increased gut permeability. Behaviorally, prolonged intake of HFD caused mice to be hypoactive and bury fewer marbles in a marble burying task; the latter was associated with significantly impaired hippocampal serotonin homeostasis. Cognitive (short-term recognition memory) function of mice was unaffected by chronic HFD feeding. Considering our prior findings of short-term (5-6 weeks) HFD-induced central (hyperactivity/anxiety and altered ventral hippocampal neurochemistry) effects and our current results, it seems that in female mice some metabolic/inflammatory dysregulations caused by HFD, such as gut permeability, appear early and persist, whereas others, such as glucose intolerance, are exaggerated with continuous HFD feeding; behaviorally, prolonged HFD consumption mainly affects locomotor activity and anxiety-like responses, likely due to the advanced obesity phenotype; neurochemically, the serotonergic system appears to be most sensitive to continued HFD feeding.